CN111710852B - Silicon negative electrode material and preparation method thereof - Google Patents
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Abstract
The invention relates to a silicon cathode material and a preparation method thereof, wherein the preparation method comprises the following steps: the preparation method comprises the following steps of (1) alternately adsorbing cationic polyelectrolyte bPEI and anionic polyelectrolyte PAA on the surface of a silicon nanoparticle to form a capsule with the silicon nanoparticle as a capsule core and the bPEI and the PAA as capsule walls, and then blending and coating the capsule, a conductive agent (acetylene black) and an adhesive (PAA aqueous solution) to prepare a silicon negative electrode material; the active material in the prepared silicon negative electrode is a capsule core-shell structure of capsule-core silicon nano particles wrapped by capsule walls formed by mutually interpenetrating and winding a cationic polyelectrolyte bPEI and an anionic polyelectrolyte PAA. The method is simple and easy to implement; the prepared silicon negative electrode material has excellent cycle stability and double charging performance.
Description
Technical Field
The invention belongs to the technical field of lithium electronic batteries, and relates to a silicon negative electrode material and a preparation method thereof.
Background
In recent years, lithium ion batteries have been regarded by academia and industry as an ideal choice for battery systems for electric vehicles and large energy storage devices. As an important component of the battery, the current commercialized lithium ion battery mainly uses graphite carbon-based negative electrode materials, but the theoretical specific capacity value of the lithium ion battery is only 372mAh g-1And the requirement of the electric automobile on the high-specific-capacity battery can not be met far away. Among the numerous non-carbon-based anode candidates, silicon has its highest theoretical specific capacity value (4200mAh g)-1) Has received great attention from the academia. Although the theoretical lithium storage capacity of silicon is 11 times that of graphite, in the actual charging and discharging process, on average, each silicon atom is combined with 4.4 lithium atoms, so that the volume change of the silicon negative electrode reaches more than 300%, and the mechanical force generated by the severe volume shrinkage and expansion can cause the active material silicon to fall off from a current collector to lose electric contact, and cause the mechanical pulverization of the silicon, and finally cause the rapid reduction of the specific capacity value.
From the perspective of structural design, the silicon particles are coated to form a core-shell structure, so that the volume change can be buffered to a great extent. One of the prior art is a solid core-shell structure, in which an active material exists in a solid state, and the outer layer is directly coated with other materials, and a coating layer designed by the structure can buffer the volume expansion of silicon particles in the lithiation process to a certain extent; the other is an egg yolk shell structure, on the basis of a solid core-shell structure, a part of the interior is hollowed by methods such as etching, and the reserved space in the interior is used for buffering the volume change of the silicon particles in the lithiation process. However, these methods have the following drawbacks:
1) the core-shell structure with a certain volume buffering function can be prepared through structural design, but no matter the core-shell structure is solid or the yolk-eggshell structure, the volume buffering effect on silicon is not reversible, and after long-time circulation, the buffering effect is invalid after the shell is broken;
2) although the reserved space of the egg-yolk shell structure can effectively buffer the volume expansion of the silicon particles, the silicon particles are mainly connected with the shell through point contact, high-speed electron transfer and lithium ion transfer are not facilitated, and the double charging performance of the silicon cathode is reduced;
3) the preparation process of the yolk-shell structure is complex and dangerous, and generally, the surface of silicon particles needs to be modified or pretreated in order to prepare the hollow structure, then the polymer shell is chemically precipitated and then sintered, and finally hydrofluoric acid is used for etching. The preparation process is complex, and the hydrofluoric acid has great danger in the use process, which is not beneficial to practical application.
Therefore, it is highly desirable to find new structures that are simpler and easier to implement to improve the overall performance of silicon anodes.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a silicon anode material and a preparation method thereof.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of a silicon negative electrode material comprises the steps of adsorbing cationic polyelectrolyte bPEI (hyperbranched polyethyleneimine) and anionic polyelectrolyte PAA (polyacrylic acid) on the surface of silicon nanoparticles alternately to form a capsule with the silicon nanoparticles as a capsule core and the polyelectrolyte bPEI and the PAA as capsule walls, and then mixing and coating the capsule serving as an active material with a conductive agent and an adhesive to prepare the silicon negative electrode material;
the number of the alternate adsorption is 5-10;
the adsorption is realized by soaking in a bPEI aqueous solution and a PAA aqueous solution, in the process of preparing the capsule, the thickness of the capsule wall is adjusted by controlling the pH values of the bPEI aqueous solution and the PAA aqueous solution, the pH value of the bPEI aqueous solution is 9.0-12.0, and the pH value of the PAA aqueous solution is 1.0-4.0.
PAA is a known linear long-chain polymer binder, and carboxyl groups on side chains of PAA can form hydrogen bonds with silicon, but the linear structure limits the number of hydrogen bonding sites. The bPEI is used as a known hyperbranched oligomer binder, a large number of amino groups and hyperbranched structures on the bPEI branched chains can form more hydrogen bonds with the oxide thin layer on the surface of the silicon nano-particles, the reversible large number of hydrogen bonds enable the bPEI and the silicon nano-particles to have stronger interface reversibility, and once the shell is damaged or the bonds on the surface of the silicon particles are broken, the hydrogen bonds can be formed again. However, the viscosity of the bPEI is smaller due to the spherical spatial three-dimensional structure of the hyperbranched polymer, the binding power and the mechanical strength of the bPEI as a binder are weakened, the defect of poor mechanical property of the hyperbranched bPEI can be effectively overcome by compounding the bPEI with the PAA, and the defect of few hydrogen bond sites of the PAA linear structure can be solved.
As a preferred technical scheme:
according to the preparation method of the silicon anode material, the conductive agent is acetylene black, and the binder is a PAA aqueous solution; the type of the conductive agent includes, but is not limited to, common graphite type conductive agents such as SUPER-P, KS-6, conductive graphite, carbon nanotubes, graphene and carbon fibers VGCF, and the type of the binder is not limited to PAA aqueous solution, and other materials such as PVA, bPEI, carboxymethyl cellulose and chitosan may be used.
The preparation method of the silicon anode material comprises the following specific steps:
(1) soaking silicon nanoparticles in a cationic polyelectrolyte bPEI aqueous solution, adsorbing a layer of cationic polyelectrolyte bPEI with positive charges on the surfaces of the silicon nanoparticles by utilizing the action of multidimensional hydrogen bonds between an oxidation layer of the silicon nanoparticles and amino groups of the bPEI, and pouring out redundant unadsorbed cationic polyelectrolyte bPEI after centrifuging in deionized water;
(2) soaking the silicon nanoparticles adsorbed with the cationic polyelectrolyte bPEI in the step (1) in an anionic polyelectrolyte PAA aqueous solution, adsorbing the anionic polyelectrolyte PAA on the surfaces of the nanoparticles through the electrostatic interaction of positive and negative charges, and pouring out the redundant unadsorbed anionic polyelectrolyte PAA after centrifuging in deionized water;
(3) repeating the adsorption process of the steps (1) and (2) for multiple times to prepare the capsule Si @ (bPEI/PAA) with the silicon nanoparticles as the capsule core and the polyelectrolyte bPEI and the PAA as the capsule wallnWherein n represents the number of repetition times, and the value range of n is 5-10;
(4) in the case of capsules Si @ (bPEI/PAA)nAdding a certain amount of cross-linking agent GA (glutaraldehyde), drying in an oven, and fixing the capsule structure through the thermal cross-linking reaction between the capsule wall materials (bPEI and PAA) and the cross-linking agent GA;
(5) and uniformly mixing the crosslinked capsules, the conductive agent and the adhesive, coating the mixture on the surface of a copper foil, and placing the copper foil in a vacuum oven to dry and dry a solvent (water in the air, water in an aqueous solution of the PAA adhesive and a small amount of water dropwise added during mixing) to prepare the silicon negative electrode material.
According to the preparation method of the silicon anode material, the concentration of the bPEI aqueous solution is 5-30 wt%, and the concentration of the PAA aqueous solution is 5-30 wt%; the mass ratio of the silicon nanoparticles to the bPEI aqueous solution and the PAA aqueous solution which are soaked each time is 1: 50-500.
In the preparation method of the silicon negative electrode material, the dispersion medium of the suspension containing the capsules in the step (4) is water, and the capsules in the suspension are Si @ (bPEI/PAA)nThe mass fraction of (A) is 5-30 wt%; capsule Si @ (bPEI/PAA)nThe mass ratio of the cross-linking agent to the cross-linking agent GA is 10-20: 1.
According to the preparation method of the silicon negative electrode material, the content of the capsules in the mixture of the crosslinked capsules, the conductive agent and the binder in the step (5) is not less than 30wt%, and the mass ratio of the conductive agent to the binder is 1: 1-4.
The invention does not adopt a composite mode of simply blending bPEI and PAA, but coats the silicon nano-particles by the adsorption between positive and negative polyions of the bPEI and the PAA. Firstly, forming a large number of hydrogen bonds between an oxide layer on the surface of the silicon nano-particles and amino groups on the bPEI to form an initial first layer; because the hyperbranched bPEI has a large number of branched chains, the amino functional groups on the branched chains attract the positive and negative charges of the carboxyl functional groups on the PAA main chain with a linear structure due to the electrostatic action, and finally the hyperbranched bPEI is wound on the linear PAA main chain to form a second layer of the capsule wall; the second layer of PAA is wound with the third layer of bPEI, and after the process is repeated for a plurality of times, a multi-layer shell is formed by interpenetrating and winding the bPEI and the PAA. The flexibility of bPEI and PAA molecular chains is improved by adjusting the pH values of bPEI solution and PAA solution, so that the thickness, the porosity and the porosity of the capsule wall are improved under the condition of not increasing the number of the deposited layers, and finally, a loose multi-layer capsule wall wrapped capsule core-shell structure which takes silicon nano particles as a capsule core and is formed by mutually winding bPEI and PAA is formed.
The volume buffering effect and the electron/ion transport properties of the capsule are closely related to the thickness of the capsule wall. The increase of the thickness of the capsule wall can improve the self-repairing capability of the capsule wall and provide enough buffer space for the volume expansion of the silicon nano particles, thereby obviously improving the cycle stability of the silicon cathode; however, the increase of the capsule wall thickness will prevent electrons and lithium ions from being smoothly transmitted to the surface of the silicon nano particles through the capsule wall, and reduce the specific capacity and rate performance of the silicon cathode, so that the capsule wall thickness of the microcapsule needs to be reasonably controlled.
When the aqueous solution of bPEI and the aqueous solution of PAA are kept neutral (pH 7), the cell wall thickness is too thin due to insufficient bending because the polyelectrolytes bPEI and PAA are kept electrically neutral, and volume expansion of the core silicon cannot be effectively buffered; when the pH value of the bPEI is 9.0-12.0 and the pH value of the PAA is 1.0-4.0, the bending degree amplitude of the bPEI and the PAA molecular chains is obviously improved due to the fact that the molecular chains of polyelectrolytes carry the same charges and repel each other, so that the thickness of the capsule wall is obviously improved under the same layer number, the increase of the thickness of the capsule wall provides enough buffer space for the volume expansion of the silicon nanoparticles, and in the lithium insertion/removal process, the capsule wall structure which is dynamically coupled through electrostatic attraction has reversibility and endows the self-repairing function of the binder material, and the capsule wall damage is automatically repaired in cooperation with multiple hydrogen bonds between the capsule wall components bPEI and the silicon nanoparticles, so that the silicon nanoparticles are continuously and effectively coated, and the cycle stability of the silicon cathode is finally improved;
when the repeated adsorption time n is more than 10, the transmission of lithium ions is blocked due to the excessively thick capsule wall, so that the double charge performance is rapidly reduced; when the repeated adsorption times n is less than 5, the capsule wall is thin due to too few capsule wall layers, so that the capsule wall is damaged; under the condition of moderate capsule wall thickness, the capsule wall thickness can effectively buffer the volume expansion of silicon, and the lithium ion transmission performance of the capsule wall component bPEI is combined with the diffusion effect of the capsule wall pore structure, so that a 'shortcut' is provided for lithium ions to rapidly reach the surface of silicon nano particles through the capsule wall, and the rate capability of the silicon cathode is effectively improved; therefore, the number n of the capsule wall layers needs to be controlled within the range of 5-10 layers to enable the capsule wall thickness to be moderate under the conditions that the pH value range of the bPEI aqueous solution is controlled to be 9.0-12.0 and the pH value range of the PAA aqueous solution is controlled to be 1.0-4.0, so that the circulation stability and the inflation performance are improved at the same time.
The invention also provides the silicon cathode material prepared by the preparation method of the silicon cathode material, wherein the active material in the silicon cathode is a compressible loose capsule core-shell structure formed by mutually interpenetrating and winding the cationic polyelectrolyte bPEI and the anionic polyelectrolyte PAA and wrapping the capsule core silicon nanoparticles by the capsule wall with certain self-repairability, the loose capsule wall is compressed to provide a buffer space for the silicon particles when the volume of the silicon nanoparticles expands, and the capsule wall damage can be repaired through the reversibility of electrostatic action after the capsule wall is damaged; after the silicon negative electrode material is assembled into the button battery, the voltage range is set to be 0.03-3V, and the voltage is set to be 250mAg-1The current density of the anode is pre-charged and discharged for 10 times to activate the silicon cathode, and the current density is 500mAg-1Performing charge and discharge cycle test on a charge and discharge tester, starting formal charge and discharge cycle test after 10 times of pre-charge and discharge cycles, wherein the specific capacity value of the negative electrode is not lower than 80% of the initial specific capacity after 100 times of charge and discharge; current densities were set to 250, 500, 1000 and 2000mAg, respectively-1Carrying out multiplying power test, when the current density reaches 2000mAg-1When the specific capacity value of the negative electrode is not less than 250mAg of current density-1Specific capacity value of time70％。
Has the advantages that:
(1) according to the preparation method of the silicon cathode material, the capsule assembly technology avoids the complex chemical synthesis or etching step related to the yolk-eggshell core-shell structure, and the silicon nanoparticles can be wrapped in a centrifugal adsorption mode to be self-assembled into the capsule structure only by utilizing the electrostatic interaction between molecules;
(2) according to the preparation method of the silicon cathode material, reversible intermolecular electrostatic acting force and hydrogen bonds enable the capsule wall formed by the binder to have reversibility, and capsule wall damage caused by volume expansion of capsule core silicon nanoparticles can be repaired repeatedly and spontaneously, so that the silicon nanoparticles are wrapped continuously;
(3) the silicon cathode material prepared by the method is different from a solid core-shell structure in that the volume expansion of silicon is buffered through the elasticity of a shell material, and the volume expansion of a yolk-eggshell structure is buffered through the space reserved between a shell and a core. Compared with the yolk shell structure, although enough buffering space energy is reserved, the structure results in that the Si as the yolk is mainly connected with the shell through point contact, which is not favorable for electron transfer and Li+The compressible loose capsule wall structure not only provides a capsule core buffer space, but also is in surface contact with the capsule core silicon nanoparticles, and does not influence electron transfer and Li+The migration, loose capsule wall structure and ionic conductivity of bPEI also facilitate electron transfer and Li+Migration, i.e. improved charging performance.
Drawings
FIG. 1 is a TEM image of a silicon anode material obtained in example 1;
FIG. 2 is a TEM image of a silicon anode material prepared in comparative example 1;
FIG. 3 is a TEM image of a silicon anode material prepared in comparative example 2;
FIG. 4 is a TEM image of a silicon anode material prepared in comparative example 3;
FIG. 5 shows charge-discharge cycle characteristics (a) and double charge characteristics (b) of a silicon negative electrode using silicon nanoparticles and capsules as active materials under different production conditions, wherein Si (bPEI10.5/PAA3) is used as a compositional expression of the capsules7For example, it shows that the pH of the aqueous bPEI solution was 10.5 and the pH of the aqueous PAA solution was 3.0 during the preparation, with a7 adsorption repeat.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
A preparation method of a silicon negative electrode material comprises the following steps:
(1) adding silicon nanoparticles with the average particle size of 160nm into a cationic polyelectrolyte bPEI aqueous solution with the concentration of 10 wt% to be soaked for 15min, adsorbing a layer of cationic polyelectrolyte bPEI with positive charges on the surface of the silicon nanoparticles, centrifuging the silicon nanoparticles in deionized water, and pouring out redundant unadsorbed cationic polyelectrolyte bPEI; wherein the mass ratio of the silicon nanoparticles to the bPEI aqueous solution is 1: 250;
(2) soaking the silicon nanoparticles adsorbed with the cationic polyelectrolyte bPEI in the step (1) in an anionic polyelectrolyte PAA aqueous solution with the concentration of 10 wt% for 15min, adsorbing the anionic polyelectrolyte PAA on the surfaces of the nanoparticles, and pouring out redundant unadsorbed anionic polyelectrolyte PAA after centrifuging in deionized water; wherein the mass ratio of the silicon nanoparticles to the PAA aqueous solution is 1: 250;
(3) repeating the adsorption process of steps (1) and (2) 7 times to obtain capsule Si @ (bPEI10.5/PAA3) with silicon nanoparticles as capsule core and bPEI and PAA as capsule wall7(ii) a In the preparation of capsules Si @ (bPEI10.5/PAA3)7In the process, the capsule wall thickness is adjusted by controlling the pH value of the bPEI aqueous solution and the PAA aqueous solutionThe pH value of the bPEI aqueous solution is 10.5, and the pH value of the PAA aqueous solution is 3.0;
(4) containing capsules Si @ (bPEI10.5/PAA3)7Adding a cross-linking agent GA into the suspension, drying in a vacuum oven at 80 ℃, and fixing the capsule structure through the thermal cross-linking reaction between the capsule wall material and the cross-linking agent GA; wherein, the capsule Si @ (bPEI10.5/PAA3) in the suspension7The mass fraction is 20 wt%, capsule Si @ (bPEI10.5/PAA3)7The mass ratio of the cross-linking agent to the cross-linking agent GA is 10: 1;
(5) and uniformly mixing the crosslinked capsule, acetylene black and a 10 wt% PAA aqueous solution, coating the mixture on the surface of a copper foil, and drying the coated copper foil in a vacuum oven to obtain the silicon negative electrode material, wherein the mass ratio of the crosslinked capsule, the acetylene black and the PAA aqueous solution is 3:1: 1.
As shown in fig. 1, the active material in the finally prepared silicon negative electrode material is a capsule core-shell structure in which capsule walls formed by mutually interpenetrating and winding positive and negative polyelectrolytes wrap capsule core silicon nanoparticles; after the silicon negative electrode material is assembled into the button battery, the voltage range is set to be 0.03-3V, and the voltage is set to be 250mAg-1The current density of the anode is pre-charged and discharged for 10 times to activate the silicon cathode, and the current density is 500mAg-1Carrying out charge-discharge cycle test, wherein after 100 times of charge-discharge, the specific capacity value of the negative electrode is 89% of the initial specific capacity; current densities were set to 250, 500, 1000 and 2000mAg, respectively-1Carrying out multiplying power test, when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 77%.
Comparative example 1
A preparation method of silicon cathode material is basically the same as that of the embodiment 1, except that in the process of preparing the capsule, the pH value of bPEI aqueous solution is controlled to be 7.0, the pH value of PAA aqueous solution is controlled to be 7.0, and the capsule Si @ (bPEI7/PAA7) is prepared7And finally, the finally prepared silicon negative electrode material TEM is shown in fig. 2, after the silicon negative electrode material is assembled into a button battery, the charging and discharging and rate testing is carried out according to the mode of the example 1, and as shown in fig. 5a, after 10 times of charging and discharging, the specific capacity is reduced to 59.3mAhg-1And is out of service; as shown in fig. 5b, at the initial current densityIs 250mAg-1Then, after 6 times of charging and discharging, the specific capacity was reduced to 57.8mAhg-1And fail. Comparing comparative example 1 with example 1, it can be seen that the cycling stability and the charging performance of the silicon anode material prepared in comparative example 1 are inferior to those of example 1 because when the aqueous solution of bPEI and the aqueous solution of PAA are kept neutral (pH 7), the wall thickness of the capsule is too thin due to insufficient bending because the polyelectrolytes bPEI and PAA keep electrical neutrality, and the volume expansion of the capsule core silicon cannot be effectively buffered; when the pH value of the bPEI is 10.5 and the pH value of the PAA is 3.0, the bending degree amplitude of the molecular chains of the bPEI and the PAA is obviously improved due to the mutual repulsion of the same charges on the molecular chain surfaces of the polyelectrolyte, so that the capsule wall thickness is obviously improved under the same layer number, the volume expansion of the capsule core silicon is effectively buffered, and the cycle stability and the double charging performance are better.
Comparative example 2
A method for preparing a silicon negative electrode material, which is substantially the same as example 1, except that the adsorption process of steps (1) and (2) is repeated 3 times in step (3), and a capsule Si @ (bPEI10.5/PAA3) is formed3And finally, the finally prepared silicon negative electrode material TEM is shown in fig. 3, after the silicon negative electrode material is assembled into a button battery, the charging and discharging and rate testing is carried out according to the mode of the example 1, and as shown in fig. 5a, after 14 times of charging and discharging, the specific capacity is reduced to 34.3mAhg-1And is out of service; as shown in FIG. 5b, at an initial current density of 250mAg-1Then, after 7 times of charging and discharging, the specific capacity was reduced to 57.4mAhg-1And fail. As can be seen from comparison of comparative example 2 with example 1, the cycle stability of the silicon anode material prepared in comparative example 2 is inferior to that of example 1 because when the adsorption process of steps (1) and (2) is repeated for a number of times n < 5, the volume expansion of the particles is not buffered due to too few numbers of capsule wall layers and the thinner capsule walls, and thus the cycle stability is inferior.
Comparative example 3
A method for preparing a silicon negative electrode material, which is substantially the same as example 1, except that the adsorption process of steps (1) and (2) is repeated 13 times in step (3) to form capsules Si @ (bPEI10.5/PAA7)13Finally obtained siliconAs shown in fig. 4, after the silicon negative electrode material is assembled into a button battery, the charge and discharge and rate test is performed in the manner of example 1, and as shown in fig. 5a, after 100 times of charge and discharge, the negative electrode specific capacity value is 81.2% of the initial specific capacity; as shown in FIG. 5b, the current densities were set to 250, 500, 1000 and 2000mAg, respectively-1Carrying out multiplying power test, when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-137.8% of the specific capacity value; comparing comparative example 3 with example 1, it can be seen that the silicon anode material prepared in comparative example 3 is much inferior to example 1 in terms of the charging performance although the cycle stability is also good, because the charging performance is rapidly decreased due to the capsule wall being too thick to block the lithium ion transport from the capsule wall to the surface of the capsule core silicon nanoparticle when the adsorption process of steps (1) and (2) is repeated for a number of times, i.e., n > 10.
Comparative example 4
A preparation method of a silicon negative electrode material does not include the steps (1) to (4), but silicon nanoparticles with the average particle size of 160nm are directly mixed with acetylene black and a PAA aqueous solution with the concentration of 10 wt% uniformly, then the mixture is coated on the surface of copper foil, and the mixture is placed in a vacuum oven to be dried to prepare the silicon negative electrode material Si/PAA, wherein the mass ratio of the silicon nanoparticles to the acetylene black to the PAA aqueous solution is 3:1: 1.
After the silicon negative electrode material was assembled into a button cell, charge-discharge cycles and rate tests were also performed in the same manner as in example 1. As shown in fig. 5a, after 7 charge-discharge cycles, the specific capacity of the silicon nanoparticle negative electrode rapidly decreased to 57.18mAhg-1I.e., it is out of service; as shown in FIG. 5b, at an initial current density of 250mAg-1Then, after 5 times of charging and discharging, the specific capacity was reduced to 36.6mAhg-1And fail.
Example 2
A preparation method of a silicon negative electrode material comprises the following steps:
(1) adding silicon nanoparticles with the average particle size of 160nm into a cationic polyelectrolyte bPEI aqueous solution with the concentration of 5 wt% to be soaked for 15min, adsorbing a layer of cationic polyelectrolyte bPEI with positive charges on the surface of the silicon nanoparticles, centrifuging the silicon nanoparticles in deionized water, and pouring out redundant unadsorbed cationic polyelectrolyte bPEI; wherein the mass ratio of the silicon nanoparticles to the bPEI aqueous solution is 1: 50;
(2) soaking the silicon nanoparticles adsorbed with the cationic polyelectrolyte bPEI in the step (1) in an anionic polyelectrolyte PAA aqueous solution with the concentration of 5 wt% for 15min, adsorbing the anionic polyelectrolyte PAA on the surfaces of the nanoparticles, and pouring out redundant unadsorbed anionic polyelectrolyte PAA after centrifuging in deionized water; wherein the mass ratio of the silicon nanoparticles to the PAA aqueous solution is 1: 50;
(3) repeating the adsorption process of steps (1) and (2) for 5 times to obtain capsule Si @ (bPEI9/PAA1) with silicon nanoparticles as capsule core and bPEI and PAA as capsule wall5(ii) a In the preparation of capsules Si @ (bPEI9/PAA1)5In the process, the thickness of the capsule wall is adjusted by controlling the pH values of a bPEI aqueous solution and a PAA aqueous solution, wherein the pH value of the bPEI aqueous solution is 9.0, and the pH value of the PAA aqueous solution is 1.0;
(4) adding a cross-linking agent GA into the suspension containing the capsules, drying in a vacuum oven at 80 ℃, and fixing the capsule structure through the thermal cross-linking reaction between the capsule wall material and the cross-linking agent GA; wherein, the capsule in the suspension is Si @ (bPEI9/PAA1)5The mass fraction of (B) is 5 wt%, capsule Si @ (bPEI9/PAA1)5The mass ratio of the cross-linking agent to the cross-linking agent GA is 10: 1;
(5) and uniformly mixing the crosslinked capsule, acetylene black and a 10 wt% PAA aqueous solution, coating the mixture on the surface of a copper foil, and drying the coated copper foil in a vacuum oven to obtain the silicon negative electrode material, wherein the mass ratio of the crosslinked capsule, the acetylene black and the PAA aqueous solution is 3:1: 1.
The active material in the finally prepared silicon negative electrode material is a capsule core-shell structure of capsule core silicon nano particles wrapped by capsule walls formed by mutually inserting and winding positive and negative polyelectrolytes; after the silicon negative electrode material is assembled into the button battery, the voltage range is set to be 0.03-3V, and the voltage is set to be 250mAg-1The current density of the anode is pre-charged and discharged for 10 times to activate the silicon cathode, and the current density is 500mAg-1Carrying out charge-discharge cycle test, wherein after 100 times of charge-discharge, the specific capacity value of the negative electrode is 85% of the initial specific capacity; will generate electricityThe flow densities were set to 250, 500, 1000 and 2000mAg, respectively-1Carrying out multiplying power test, when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 75%.
Example 3
A preparation method of a silicon negative electrode material comprises the following steps:
(1) adding silicon nanoparticles with the average particle size of 160nm into a cationic polyelectrolyte bPEI aqueous solution with the concentration of 30wt% to be soaked for 15min, adsorbing a layer of cationic polyelectrolyte bPEI with positive charges on the surface of the silicon nanoparticles, centrifuging the silicon nanoparticles in deionized water, and pouring out redundant unadsorbed cationic polyelectrolyte bPEI; wherein the mass ratio of the silicon nanoparticles to the bPEI aqueous solution is 1: 500;
(2) soaking the silicon nanoparticles adsorbed with the cationic polyelectrolyte bPEI in the step (1) in an anionic polyelectrolyte PAA aqueous solution with the concentration of 30wt% for 15min, adsorbing the anionic polyelectrolyte PAA on the surfaces of the nanoparticles, and pouring out redundant unadsorbed anionic polyelectrolyte PAA after centrifuging in deionized water; wherein the mass ratio of the silicon nanoparticles to the PAA aqueous solution is 1: 500;
(3) repeating the adsorption process of steps (1) and (2) 10 times to obtain capsule Si @ (bPEI12/PAA4) with silicon nanoparticles as capsule core and bPEI and PAA as capsule wall10(ii) a In the preparation of capsules Si @ (bPEI12/PAA4)10In the process, the thickness of the capsule wall is adjusted by controlling the pH values of a bPEI aqueous solution and a PAA aqueous solution, wherein the pH value of the bPEI aqueous solution is 12.0, and the pH value of the PAA aqueous solution is 4.0;
(4) adding a cross-linking agent GA into the suspension containing the capsules, drying in a vacuum oven at 80 ℃, and fixing the capsule structure through the thermal cross-linking reaction between the capsule wall material and the cross-linking agent GA; wherein, the capsule in the suspension Si @ (bPEI/PAA)10The mass fraction of (B) is 30wt%, and the capsule Si @ (bPEI12/PAA4)10The mass ratio of the cross-linking agent to the cross-linking agent GA is 20: 1;
(5) and uniformly mixing the crosslinked capsule, acetylene black and a 10 wt% PAA aqueous solution, coating the mixture on the surface of a copper foil, and drying the coated copper foil in a vacuum oven to obtain the silicon negative electrode material, wherein the mass ratio of the crosslinked capsule, the acetylene black and the PAA aqueous solution is 3:1: 1.
The active material in the finally prepared silicon negative electrode material is a capsule core-shell structure of capsule core silicon nano particles wrapped by capsule walls formed by mutually inserting and winding positive and negative polyelectrolytes; after the silicon negative electrode material is assembled into the button battery, the voltage range is set to be 0.03-3V, and the voltage is set to be 250mAg-1The current density of the anode is pre-charged and discharged for 10 times to activate the silicon cathode, and the current density is 500mAg-1Carrying out charge-discharge cycle test, wherein after 100 times of charge-discharge, the specific capacity value of the negative electrode is 84% of the initial specific capacity; current densities were set to 250, 500, 1000 and 2000mAg, respectively-1Carrying out multiplying power test, when the current density reaches 2000mAg-1The specific capacity of the negative electrode was 250mAg in terms of current density-1The specific capacity value is 70%.
Claims (5)
1. A silicon negative electrode material is characterized in that: the active material in the silicon negative electrode is a capsule core-shell structure, wherein the capsule core-shell structure is formed by mutually interpenetrating and winding a cationic polyelectrolyte bPEI and an anionic polyelectrolyte PAA, and silicon nano particles are wrapped by the capsule wall; after the silicon negative electrode material is assembled into the button battery, the voltage range is set to be 0.03-3V, and the voltage is set to be 250mAg-1The current density of the anode is pre-charged and discharged for 10 times to activate the silicon cathode, and the current density is 500mAg-1Carrying out charge-discharge cycle test, wherein after 100 times of charge-discharge, the specific capacity value of the negative electrode is not lower than 80% of the initial specific capacity; current densities were set to 250, 500, 1000 and 2000mAg, respectively-1Carrying out multiplying power test, when the current density reaches 2000mAg-1When the specific capacity value of the negative electrode is not less than 250mAg of current density-170% of the specific capacity value;
the preparation method of the silicon negative electrode material comprises the following steps:
(1) soaking silicon nanoparticles in a cationic polyelectrolyte bPEI aqueous solution, adsorbing a cationic polyelectrolyte bPEI on the surfaces of the silicon nanoparticles, centrifuging in deionized water, and pouring out redundant unadsorbed cationic polyelectrolyte bPEI;
(2) soaking the silicon nanoparticles adsorbed with the cationic polyelectrolyte bPEI in the step (1) in an anionic polyelectrolyte PAA aqueous solution, adsorbing the anionic polyelectrolyte PAA on the surfaces of the nanoparticles, and pouring out redundant unadsorbed anionic polyelectrolyte PAA after centrifuging in deionized water;
(3) repeating the steps (1) and (2) for multiple times to obtain the capsule Si @ (bPEI/PAA) with the silicon nanoparticles as the capsule core and the bPEI and the PAA as the capsule wallnWherein n represents the number of repetition times, and the value range of n is 5-10;
(4) in the case of capsules Si @ (bPEI/PAA)nAdding a certain amount of cross-linking agent GA into the suspension, drying in an oven, and fixing the capsule structure through the thermal cross-linking reaction between the capsule wall material and the cross-linking agent GA;
(5) uniformly mixing the crosslinked capsule, the conductive agent and the adhesive, coating the mixture on the surface of a copper foil, and placing the copper foil in a vacuum oven for drying to obtain a silicon negative electrode material;
the average particle diameter of the silicon nanoparticles is 160 nm;
the pH value of the bPEI aqueous solution is 9.0-12.0, and the pH value of the PAA aqueous solution is 1.0-4.0.
2. The silicon negative electrode material as claimed in claim 1, wherein the conductive agent is acetylene black, and the binder is an aqueous PAA solution.
3. The silicon anode material of claim 1, wherein the concentration of the bPEI aqueous solution is 5-30 wt%, and the concentration of the PAA aqueous solution is 5-30 wt%; the mass ratio of the silicon nanoparticles to the bPEI aqueous solution and the PAA aqueous solution which are soaked each time is 1: 50-500.
4. The silicon negative electrode material as claimed in claim 1, wherein the capsule Si @ (bPEI/PAA) in the suspension of step (4)nThe mass fraction of (A) is 5-30 wt%; capsule Si @ (bPEI/PAA)nThe mass ratio of the cross-linking agent to the cross-linking agent GA is 10-20: 1.
5. The silicon negative electrode material as claimed in claim 1, wherein the content of the capsules in the mixture of the crosslinked capsules, the conductive agent and the binder in step (5) is not less than 30wt%, and the mass ratio of the conductive agent to the binder is 1: 1-4.
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